1. Field of the Invention
The present invention relates to blood pressure measurement devices and control methods for blood pressure measurement devices, and particularly relates to blood pressure measurement devices configured to measure a blood pressure during inflation of a cuff and to control methods for such blood pressure measurement devices.
2. Description of the Related Art
An electronic blood pressure meter that uses an oscillometric technique is known as a typical electronic blood pressure meter. In an electronic blood pressure meter that uses the oscillometric technique, a manchette containing an air bladder is uniformly wrapped around a part of a body, and changes in the volume of an arterial vessel pressurized by inflating/deflating the air bladder with air are obtained as changes in the amplitude of the pressure in the air bladder (a cuff pressure), which are then used to calculate a blood pressure. To measure the blood pressure accurately while inflating the cuff, it is necessary to properly control the speed at which the pressure within the cuff is increased. For example, it is necessary to inflate the cuff at a constant speed.
JP 2009-74418A proposes a piezoelectric micro-pump driven using a piezoelectric element, and discusses applying such a micro-pump in an electronic blood pressure meter. Meanwhile, JP 2010-255447A, JP 2010-162487A, and so on propose setting a driving frequency according to the material of a piezoelectric element and a diaphragm and carrying out control near the driving frequency.
Although conventional blood pressure meter pumps control pump output through pulse width modulation (PWM) control, piezoelectric pump output control is generally considered to be performed by driving the pump at the driving frequency and controlling the output through voltage control.
However, such piezoelectric pumps have had the following problems: (1) the precision of voltage control corresponds to the precision of the pump output, and it is thus necessary to increase the precision of voltage control in order to control the inflation speed at a proper speed; (2) attempting to increase the precision of voltage control results in an increase in the number of components and the like for setting the resolution, leading to an increase in circuitry costs; and (3) although increasing the resolution by adding AM modulation to the voltage control can be considered, such a system is affected by pulsations, ambient sounds, and the like when installed in a blood pressure meter.